Mobile communication system, user terminal, and processor

ABSTRACT

A UE  100 - 1  and a UE  200 - 2  perform D2D communication that is direct device to device communication. The UE  100 - 1  transmits a D2D termination preliminary notification indicating that termination of the D2D communication is wished to the UE  100 - 2  during the D2D communication. The UE  100 - 1  terminates the D2D communication after transmitting the D2D termination preliminary notification.

TECHNICAL FIELD

The present invention relates to a mobile communication system, a userterminal, and a processor supporting device to device (D2D)communication.

BACKGROUND ART

In 3GPP (3rd Generation Partnership Project) which is a project aimingto standardize a mobile communication system, it has been studied tointroduce device to device (D2D) communication as a new feature afterRelease 12 (see Non Patent Document 1).

In D2D communication, a plurality of neighboring user terminals performsdirect communication without passing through a base station. That is, adata path of D2D communication does not pass through a base station. Onthe other hand, a data path for normal communication (cellularcommunication) in a mobile communication system passes through a basestation.

PRIOR ART DOCUMENT Non-Patent Document

-   Non Patent Document 1: 3GPP technical report “TR 22.803 V12.1.0”,    March 2013

SUMMARY OF THE INVENTION

However, when another user terminal that is a counterpart terminal forD2D communication terminates D2D communication without permission, auser terminal does not recognize that the D2D communication becomesimpossible. Due to this, there is a problem that the user terminalmaintains a waiting state for receiving data from the another userterminal or the user terminal transmits data to the another userterminal even when the another user terminal does not receive data.

In view of the above, the present invention provides a mobilecommunication system, a user terminal, and a processor, which canprevent the user terminal from performing useless processing bytermination of D2D communication of a counterpart terminal in D2Dcommunication.

A mobile communication system according to a first aspect comprises: afirst user terminal and a second user terminal configured to perform D2D(Device to Device) communication that is direct device to devicecommunication. The first user terminal transmits a D2D terminationpreliminary notification indicating that the first user terminal wishestermination of the D2D communication to the second user terminal duringthe D2D communication. The first user terminal terminates the D2Dcommunication after transmitting the D2D termination preliminarynotification.

A user terminal according to a second aspect performs D2D (Device toDevice) communication that is direct device to device communication withanother user terminal. The user terminal comprises: a controllerconfigured to transmit a D2D termination preliminary notificationindicating that the user terminal wishes termination of the D2Dcommunication to the another user terminal during the D2D communication.The controller terminates the D2D communication after transmitting theD2D termination preliminary notification.

A processor according to a third aspect is provided in a user terminalconfigured to perform D2D (Device to Device) communication that isdirect device to device communication with another user terminal. Theprocessor performs: a process of transmitting a D2D terminationpreliminary notification indicating that the user terminal wishestermination of the D2D communication to the another user terminal duringthe D2D communication; and a process of terminating the D2Dcommunication after transmission of the D2D termination preliminarynotification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of an LTE systemaccording to a first embodiment to a third embodiment.

FIG. 2 is a block diagram of a UE according to a first embodiment to athird embodiment.

FIG. 3 is a block diagram of an eNB according to a first embodiment to athird embodiment.

FIG. 4 is a protocol stack diagram of radio interface according to afirst embodiment to a third embodiment.

FIG. 5 is a configuration diagram of a radio frame according to a firstembodiment to a third embodiment.

FIG. 6 is a diagram for describing D2D communication according to afirst embodiment to a third embodiment.

FIG. 7 is a sequence diagram 1 illustrating an operation pattern 1according to a first embodiment.

FIG. 8 is a sequence diagram 2 illustrating an operation pattern 1according to a first embodiment.

FIG. 9 is a sequence diagram illustrating an operation pattern 2according to a first embodiment.

FIG. 10 is a sequence diagram 1 illustrating an operation pattern 3according to a first embodiment.

FIG. 11 is a sequence diagram 2 illustrating an operation pattern 3according to a first embodiment.

FIG. 12 is a sequence diagram illustrating an operation according to asecond embodiment.

FIG. 13 is a sequence diagram illustrating an operation pattern 1according to a third embodiment.

FIG. 14 is a sequence diagram illustrating an operation pattern 2according to a third embodiment.

FIG. 15 is a sequence diagram illustrating an operation pattern 3according to a third embodiment.

DESCRIPTION OF THE EMBODIMENT Overview of Embodiment

A mobile communication system according to a first embodiment to a thirdembodiment comprises: a first user terminal and a second user terminalconfigured to perform D2D (Device to Device) communication that isdirect device to device communication. The first user terminal transmitsa D2D termination preliminary notification indicating that the firstuser terminal wishes termination of the D2D communication to the seconduser terminal during the D2D communication. The first user terminalterminates the D2D communication after transmitting the D2D terminationpreliminary notification.

In a first embodiment, the first user terminal transmits the D2Dtermination preliminary notification when data to be transmitted to thesecond user does not exist in the D2D communication.

In a first embodiment, a case where data to be transmitted does notexist is a case where the first user terminal terminates an applicationused in the D2D communication.

In a first embodiment, the second user terminal, which has received theD2D termination preliminary notification, transmits a D2D continuityrequest requesting continuity of the D2D communication to the first userterminal when it is determined that continuity of the D2D communicationis wished.

In a first embodiment, the second user terminal, which has received theD2D termination preliminary notification, determines that continuity ofthe D2D communication is wished, when data to be transmitted to thefirst user terminal exists or when the second user terminal is waitingfor reception of a specific signal associated with the first userterminal.

In a first embodiment, the first user terminal, which has received theD2D continuity request, is prohibited from transmitting the D2Dtermination preliminary notification until a first predetermined periodhas elapsed after reception of the D2D continuity request.

In a first embodiment, the first user terminal terminates the D2Dcommunication when the first user terminal does not receive the D2Dcontinuity request until the second predetermined period has elapsedafter transmission of the D2D termination preliminary notification.

In a first embodiment, the second user terminal, which has received theD2D termination preliminary notification, transmits a D2D terminationpermission notification permitting termination of the D2D communicationto the first user terminal when the second user terminal permits thefirst user terminal to terminate the D2D communication.

In a second embodiment, the first user terminal measures a D2Dcommunication time indicating a time during which the D2D communicationis continued, or a D2D data amount indicating an amount of datatransmitted and/or received in the D2D communication. The first userterminal transmits D2D measurement information indicating at least oneof the D2D communication time and the D2D data amount to a network, whenthe first user terminal terminates the D2D communication.

In a second embodiment, the first user terminal measures the D2Dcommunication time or the D2D data amount when performing the D2Dcommunication by using a frequency band managed by an operator.

In a third embodiment, it comprises an anchor terminal configured torepresentatively perform communication with a network for the D2Dcommunication. The anchor terminal is the second user terminal oranother user terminal which performs the D2D communication. The firstuser terminal measures a D2D communication time indicating a time duringwhich the D2D communication is continued, or a D2D data amountindicating an amount of data transmitted and/or received in the D2Dcommunication. The first user terminal transmits D2D measurementinformation indicating at least one of the D2D communication time andthe D2D data amount to the anchor terminal, when the first user terminalterminates the D2D communication.

In a third embodiment, it comprises an anchor terminal configured torepresentatively perform communication with a network for the D2Dcommunication. The anchor terminal is another user terminal whichperforms the D2D communication. The first user terminal transmits theD2D termination preliminary notification to the second user terminalthrough the anchor terminal. The second user terminal transmits the D2Dcontinuity request to the first user terminal through the anchorterminal.

In a third embodiment, it comprising an anchor terminal configured torepresentatively perform communication with a network for the D2Dcommunication. The anchor terminal is another user terminal whichperforms the D2D communication. The first user terminal transmits theD2D termination preliminary notification to the second user terminalthrough the anchor terminal. The second user terminal transmits the D2Dtermination permission notification to the first user terminal throughthe anchor terminal.

A user terminal according to a first embodiment to a third embodimentperforms D2D (Device to Device) communication that is direct device todevice communication with another user terminal. The user terminalcomprises: a controller configured to transmit a D2D terminationpreliminary notification indicating that the user terminal wishestermination of the D2D communication to the another user terminal duringthe D2D communication. The controller terminates the D2D communicationafter transmitting the D2D termination preliminary notification.

A processor according to a first embodiment to a third embodiment isprovided in a user terminal configured to perform D2D (Device to Device)communication that is direct device to device communication with anotheruser terminal. The processor performs: a process of transmitting a D2Dtermination preliminary notification indicating that the user terminalwishes termination of the D2D communication to the another user terminalduring the D2D communication; and a process of terminating the D2Dcommunication after transmission of the D2D termination preliminarynotification.

First Embodiment

Hereinafter, a description will be provided for an embodiment in a casewhere the present invention is applied to an LTE system.

(System Configuration)

FIG. 1 is a configuration diagram of an LTE system according to thefirst embodiment. As illustrated in FIG. 1, the LTE system includes UEs(User Equipment) 100, EUTRAN (Evolved-UMTS Terrestrial Radio AccessNetwork) 10, and EPC (Evolved Packet Core) 20.

The UE 100 corresponds to a user terminal. The UE 100 is a mobilecommunication device and performs radio communication with a connectingcell (serving cell). A configuration of the UE 100 will be describedbelow in detail.

The E-UTRAN 10 corresponds to a radio access network. The E-UTRAN 10includes eNBs 200 (evolved Node-B). The eNB 200 corresponds to a basestation. The eNBs 200 are connected to one another via an X2 interface.A configuration of the eNB 200 will be described below in detail.

Each eNB 200 manages one or a plurality of cells and performs radiocommunication with the UE 100 which establishes a connection with thecell of the eNB 200. The eNB 200, for example, has a radio resourcemanagement (RRM) function, a routing function of user data, and ameasurement control function for mobility control and scheduling. The“cell” is used as a term indicating a minimum unit of a radiocommunication area, and is also used as a term indicating a function ofperforming radio communication with the UE 100.

The EPC 20 corresponds to a core network. The E-UTRAN 10 and the EPC 20configure a network of the LTE system. The EPC 20 includes a pluralityof MME (Mobility Management Entity)/S-GWs (Serving-Gateway) 300. The MMEperforms various mobility controls and the like for the UE 100. The S-GWperforms transfer control of user data. The MME/S-GW 300 is connected toeNB 200s via an S1 interface.

FIG. 2 is a block diagram of the UE 100. As illustrated in FIG. 2, theUE 100 includes a plurality of antennas 101, a radio transceiver 110, auser interface 120, a GNSS (Global Navigation Satellite System) receiver130, a battery 140, a memory 150, and a processor 160. The memory 150and the processor 160 configure a controller. The UE 100 may not havethe GNSS receiver 130. Furthermore, the memory 150 may be integrallyformed with the processor 160, and this set (that is, a chip set) may becalled a processor 160′.

The plurality of antennas 101 and the radio transceiver 110 are used totransmit and receive a radio signal. The radio transceiver 110 convertsa baseband signal (transmission signal) output from the processor 160into the radio signal, and transmits the radio signal from the pluralityof antennas 101. Furthermore, the radio transceiver 110 converts theradio signal received by the plurality of antennas 101 into the basebandsignal (reception signal), and outputs the baseband signal to theprocessor 160.

The user interface 120 is an interface with a user carrying the UE 100,and includes, for example, a display, a microphone, a speaker, andvarious buttons. The user interface 120 receives an operation from auser and outputs a signal indicating the content of the operation to theprocessor 160. The GNSS receiver 130 receives a GNSS signal in order toobtain location information indicating a geographical location of the UE100, and outputs the received signal to the processor 160. The battery140 accumulates a power to be supplied to each block of the UE 100.

The memory 150 stores a program to be executed by the processor 160 andinformation to be used for a process by the processor 160. The processor160 includes a baseband processor that performs modulation anddemodulation, encoding and decoding and the like on the baseband signal,and a CPU (Central Processing Unit) that performs various processes byexecuting the program stored in the memory 150. The processor 160 mayfurther include a codec that performs encoding and decoding on sound andvideo signals. The processor 160 executes various processes and variouscommunication protocols, which will be described later.

FIG. 3 is a block diagram of the eNB 200. As illustrated in FIG. 3, theeNB 200 includes a plurality of antennas 201, a radio transceiver 210, anetwork interface 220, a memory 230, and a processor 240. The memory 230and the processor 240 constitute a controller.

The plurality of antennas 201 and the radio transceiver 210 are used totransmit and receive a radio signal. The radio transceiver 210 convertsa baseband signal (transmission signal) output from the processor 240into the radio signal, and transmits the radio signal from the pluralityof antennas 201. Furthermore, the radio transceiver 210 converts theradio signal received by the plurality of antennas 201 into the basebandsignal (reception signal), and outputs the baseband signal to theprocessor 240.

The network interface 220 is connected to the neighboring eNB 200 viathe X2 interface and is connected to the MME/S-GW 300 via the S1interface. The network interface 220 is used in communication performedon the X2 interface and communication performed on the S1 interface.

The memory 230 stores a program to be executed by the processor 240 andinformation to be used for a process by the processor 240. The processor240 includes the baseband processor that performs modulation anddemodulation, encoding and decoding and the like on the baseband signaland a CPU that performs various processes by executing the programstored in the memory 230. The processor 240 executes various processesand various communication protocols, which will be described later.

FIG. 4 is a protocol stack diagram of a radio interface in the LTEsystem. As illustrated in FIG. 4, the radio interface protocol isclassified into a layer 1 to a layer 3 of an OSI reference model,wherein the layer 1 is a physical (PHY) layer. The layer 2 includes anMAC (Media Access Control) layer, an RLC (Radio Link Control) layer, anda PDCP (Packet Data Convergence Protocol) layer. The layer 3 includes anRRC (Radio Resource Control) layer.

The PHY layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. Between the PHY layer of the UE 100 and the PHY layer of theeNB 200, user data and control signal are transmitted via the physicalchannel.

The MAC layer performs priority control of data, and a retransmissionprocess and the like by hybrid ARQ (HARQ). Between the MAC layer of theUE 100 and the MAC layer of the eNB 200, user data and control signalare transmitted via a transport channel. The MAC layer of the eNB 200includes a transport format of an uplink and a downlink (a transportblock size and a modulation and coding scheme) and a scheduler fordetermining a resource block to be assigned to the UE100.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the PHY layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, user data andcontrol signal are transmitted via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane dealing with a controlsignal. Between the RRC layer of the UE 100 and the RRC layer of the eNB200, a control signal (an RRC message) for various types of setting istransmitted. The RRC layer controls the logical channel, the transportchannel, and the physical channel in response to establishment,re-establishment, and release of a radio bearer. When there is anconnection (RRC connection) between the RRC of the UE 100 and the RRC ofthe eNB 200, the UE 100 is in a connected state (an RRC connectedstate), and when there is no connection (no RRC connection), the UE 100is in an idle state (an RRC idle state).

An NAS (Non-Access Stratum) layer positioned above the RRC layerperforms session management, mobility management and the like.

FIG. 5 is a configuration diagram of a radio frame used in the LTEsystem. In the LTE system, OFDMA (Orthogonal Frequency DivisionMultiplexing Access) is applied to a downlink (DL), and SC-FDMA (SingleCarrier Frequency Division Multiple Access) is applied to an uplink(UL), respectively.

As illustrated in FIG. 5, the radio frame is configured by 10 subframesarranged in a time direction. Each subframe is configured by two slotsarranged in the time direction. Each subframe has a length of 1 ms andeach slot has a length of 0.5 ms. Each subframe includes a plurality ofresource blocks (RB) in a frequency direction, and a plurality ofsymbols in the time direction. Each resource block includes a pluralityof subcarriers in the frequency direction. A radio resource unit isconfigured by one subcarrier and one symbol and one subcarrier.

Among radio resources allocated to the UE 100, a frequency resource canbe configured by a resource block and a time resource can be configuredby a subframe (or slot).

In the DL, an interval of several symbols from the head of each subframeis a region used as a physical downlink control channel (PDCCH) formainly transmitting a control signal. Furthermore, the other portion ofeach subframe is a region available as a physical downlink sharedchannel (PDSCH) for mainly transmitting user data.

In the UL, both ends in the frequency direction of each subframe areregions used as a physical uplink control channel (PUCCH) for mainlytransmitting a control signal. The central portion of each subframe is aregion available as a physical uplink shared channel (PUSCH) for mainlytransmitting user data.

(D2D Communication)

An LTE system according to a first embodiment supports D2D communicationthat is direct device to device communication (UE to UE communication).In this case, the D2D communication will be described in comparison withcellular communication that is normal communication of the LTE system.The cellular communication is a communication mode in which a data pathpasses through a network (E-UTRAN 10, EPC 20). The data path refers to acommunication path of user data. On the contrary, the D2D communicationis a communication mode in which a data path established between UEsdoes not pass through a network.

FIG. 6 is a diagram for describing D2D communication.

As illustrated in FIG. 6, in the D2D communication, a data path does notpass through an eNB 200. A UE 100-1 and a UE 100-2 which are adjacent toeach other perform direct radio communication with low transmissionpower in a cell of the eNB 200. In this way, the UE 100-1 and the UE100-2 which are adjacent to each other perform direct radiocommunication with low transmission power, reducing power consumption inthe UEs 100 and reducing interference to an adjacent cell. Also, thereare a case where D2D communication is performed in a state in which theUE 100 in an idle state and a case where D2D communication is performedin a state in which the UE 100 in a connected state.

(Operation According to First Embodiment)

(1) Operation Overview

An LTE system according to a first embodiment includes a UE 100-1 (firstuser terminal) and a UE 100-2 (second user terminal), which perform D2Dcommunication that is direct device to device communication. The UE100-1 transmits a D2D termination preliminary notification indicatingthat termination of the D2D communication is wished to the UE 100-2during D2D communication. The UE 100-1 terminates D2D communicationafter transmitting the D2D termination preliminary notification.Therefore, the UE 100-2 can know that the UE 100-1 wishes termination ofD2D communication. Accordingly, it is possible to prevent the UE 100-2from terminating D2D communication unexpectedly.

In the first embodiment, when data to be transmitted to the UE 100-2 inD2D communication does not exist, the UE 100-1 transmits the D2Dtermination preliminary notification. A case where the data to betransmitted does not exist may be a case where the UE 100-1 terminatesan application used in D2D communication. Therefore, the UE 100-1 canappropriately determine whether to notify the UE 100-2 that the UE 100-1wishes termination of D2D communication.

In the first embodiment, when determining that continuity of the D2Dcommunication is wished, the UE 100-2 which has received the D2Dtermination preliminary notification transmits the D2D continuityrequest requesting D2D communication to the UE 100-1. Therefore, the UE100-1 can grasp that the UE 100-2 wishes continuity of D2Dcommunication. Accordingly, it is possible to continue D2D communicationwithout termination of D2D communication according to the wish of the UE100-2.

In the first embodiment, when data to be transmitted to the UE 100-1exists or when the UE 100-2 is waiting for reception of a specificsignal associated with the UE 100-1, the UE 100-2, which has receivedthe D2D termination preliminary notification, determines that continuityof D2D communication with the UE 100-1 is wished. The specific signalis, for example, a response signal from the UE 100-1 in an applicationused in the D2D communication. Therefore, the UE 100-2 can appropriatelydetermine whether to notify the UE 100-1 that the UE 100-2 wishescontinuity of D2D communication.

In the first embodiment, the UE 100-1, which has received the D2Dcontinuity request, is prohibited from transmitting a D2D terminationpreliminary notification until the first predetermined period haselapsed after reception of the D2D continuity request. Therefore, it ispossible to reduce possibility that transmission of the D2D terminationpreliminary notification by the UE 100-1 would be useless, and suppressincreases in a processing load and a resource use amount, due totransmission of the D2D termination preliminary notification.

In the first embodiment, the UE 100-1 terminates the D2D communicationwhen the UE 100-1 does not receive the D2D continuity request until thesecond predetermined period has elapsed after transmission of the D2Dtermination preliminary notification. Therefore, when it can beconsidered that the UE 100-2 does not wish continuity of D2Dcommunication, the UE 100-1 can terminate D2D communication.

Alternatively, in the first embodiment, the UE 100-2 which has receivedthe D2D termination preliminary notification transmits a D2D terminationpermission notification permitting termination of D2D communication tothe UE 100-1 when permitting the UE 100-1 to terminate D2Dcommunication. Therefore, in a state in which the UE 100-1 has confirmedthat the UE 100-2 does not wish continuity of D2D communication, the UE100-1 can terminate D2D communication.

Hereinafter, operation patterns 1 to 3 according to a first embodimentwill be described. In the operation patterns 1 to 3, it is assumed thatthree UEs 100 (UE 100-1 to UE 100-3) perform D2D communication. Itshould be noted that the number of UEs 100 which perform D2Dcommunication may be two or more than three.

(2) Operation Pattern 1

FIG. 7 is a sequence diagram 1 illustrating an operation pattern 1according to a first embodiment. In this case, it is assumed that eachUE 100 performs D2D communication in an idle state.

As illustrated in FIG. 7, in step S101, a UE 100-1 to a UE 100-3 whichare in an idle state perform D2D communication.

In step S102, the UE 100-1 transmits a D2D termination preliminarynotification indicating that termination of D2D communication is wishedto the UE 100-2 and the UE 100-3 during the D2D communication. When datato be transmitted to the UE 100-2 in D2D communication does not exist,the UE 100-1 transmits the D2D termination preliminary notification. Inthis regard, a case where the data to be transmitted does not exist maybe a case where the UE 100-1 terminates an application used in D2Dcommunication. Also, when the UE 100-1 transmits the D2D terminationpreliminary notification, the UE 100-1 starts a timer corresponding to asecond predetermined period.

The UE 100-2 and the UE 100-3 which have been received the D2Dtermination preliminary notification determine whether continuity of D2Dcommunication with the UE 100-1 is wished. For example, when data to betransmitted to the UE 100-1 exists or when the UE 100-2 and the UE 100-3is waiting for reception of a specific signal associated with the UE100-1, the UE 100-2 and the UE 100-3 determine that continuity of D2Dcommunication with the UE 100-1 is wished. In this case, a descriptionwill be given under the assumption that the UE 100-2 and the UE 100-3 donot wish continuity of D2D communication with the UE 100-1.

In step S103, when confirming that the timer corresponding to the secondpredetermined period is expired, the UE 100-1 terminates the D2Dcommunication. As described above, in the operation pattern 1, the UE100-1 terminates the D2D communication when the UE 100-1 does notreceive the D2D continuity request until the second predetermined periodhas elapsed after transmission of the D2D termination preliminarynotification.

On the other hand, in step S104, the UE 100-2 and the UE 100-3 continuethe D2D communication.

Although it is assumed in FIG. 7 that the UE 100 performs the D2Dcommunication in an idle state, the sequence of FIG. 7 may be changed ina case where the UE 100 performs the D2D communication in a connectedstate.

FIG. 8 is a sequence diagram 2 illustrating an operation pattern 1according to a first embodiment. In this case, differences from FIG. 7in a case where each UE 100 performs D2D communication in a connectedstate will be mainly described.

As illustrated in FIG. 8, in step S101, a UE 100-1 to a UE 100-3, whichare in a connected state to a cell of an eNB 200, perform D2Dcommunication.

In step S102, the UE 100-1 transmits a D2D termination preliminarynotification indicating that termination of D2D communication is wishedto the UE 100-2 and the UE 100-3 during the D2D communication. Also,when the UE 100-1 transmits the D2D termination preliminarynotification, the UE 100-1 starts a timer corresponding to a secondpredetermined period.

The UE 100-2 and the UE 100-3, which have been received the D2Dtermination preliminary notification, determine whether continuity ofD2D communication with the UE 100-1 is wished. In this case, adescription will be given under the assumption that the UE 100-2 and theUE 100-3 do not wish continuity of D2D communication with the UE 100-1.

In step S103-1, when confirming that a timer corresponding to a secondpredetermined period is expired, the UE 100-1 transmits a D2Dtermination completion notification indicating completion of processingto terminate the D2D communication to the eNB 200. Also, in step S103-2,the UE 100-1 terminates the D2D communication. The eNB 200, which hasreceived the D2D termination completion notification from the UE 100-1,can terminate control of the D2D communication (resource allocation orthe like) for the UE 100-1.

On the other hand, in step S104, the UE 100-2 and the UE 100-3 continuethe D2D communication.

(3) Operation Pattern 2

FIG. 9 is a sequence diagram illustrating an operation pattern 2according to a first embodiment. In this case, it is assumed that eachUE 100 performs D2D communication in an idle state or a connected state.Also, a description for the same operation as FIG. 7 will beappropriately omitted.

As illustrated in FIG. 9, in step S111, a UE 100-1 to a UE 100-3 performD2D communication.

In step S112, the UE 100-1 transmits a D2D termination preliminarynotification indicating that termination of D2D communication is wishedto the UE 100-2 and the UE 100-3 during the D2D communication.

The UE 100-2 and the UE 100-3 which have been received the D2Dtermination preliminary notification determine whether D2D communicationwith the UE 100-1 is wished to be continued. In this case, a descriptionwill be given under the assumption that the UE 100-2 wishes continuityof D2D communication with the UE 100-1.

In step S113, the UE 100-2 transmits a D2D continuity request requestingcontinuity of the D2D communication to the UE 100-1. The UE 100-1, whichhas received the D2D continuity request, determines to continue the D2Dcommunication without termination of the D2D communication according toa wish from the UE 100-2. Also, when the UE 100-1 receives the D2Dcontinuity request, the UE 100-1 starts a timer corresponding to a firstpredetermined period. The UE 100-1, which has received the D2Dcontinuity request, is prohibited from transmitting a D2D terminationpreliminary notification until the first predetermined period haselapsed after reception of the D2D continuity request.

In step S114, the UE 100-1 to the UE 100-3 continue the D2Dcommunication. Also, when a request for D2D communication with the UE100-3 not the UE 100-2 is again generated by the UE 100-1 within apredetermined time, a termination cancelling request (which is D2Dcontinuity request) may be transmitted to the UE 100-2 and the UE 100-3.

(4) Operation Pattern 3

FIG. 10 is a sequence diagram 1 illustrating an operation pattern 3according to a first embodiment. In this case, it is assumed that eachUE 100 performs D2D communication in an idle state. Also, a descriptionfor the same operation as FIG. 7 will be appropriately omitted.

As illustrated in FIG. 10, in step S121, a UE 100-1 to a UE 100-3 whichare in an idle state perform D2D communication.

In step S122, the UE 100-1 transmits a D2D termination preliminarynotification indicating that termination of D2D communication is wishedto the UE 100-2 and the UE 100-3 during the D2D communication. In theoperation pattern 3, when the UE 100-1 transmits the D2D terminationpreliminary notification, the UE 100-1 may not start a timercorresponding to a second predetermined period.

The UE 100-2 and the UE 100-3 which have been received the D2Dtermination preliminary notification determine whether D2D communicationwith the UE 100-1 is wished to be continued. In this case, a descriptionwill be given under the assumption that the UE 100-2 and the UE 100-3 donot wish continuity of D2D communication with the UE 100-1.

In step S123, the UE 100-2 and the UE 100-3 transmit a D2D terminationpermission notification permitting termination of the D2D communicationto the UE 100-1.

In step S124, the UE 100-1, which has received the D2D terminationpermission notification from the UE 100-2 and the UE 100-3 terminatesthe D2D communication.

On the other hand, in step S125, the UE 100-2 and the UE 100-3 continuethe D2D communication.

Although it is assumed in FIG. 10 that the UE 100 performs the D2Dcommunication in an idle state, the sequence of FIG. 10 may be changedin a case where the UE 100 performs the D2D communication in aconnection state.

FIG. 11 is a sequence diagram 2 illustrating an operation pattern 3according to a first embodiment. In this case, differences from FIG. 10in a case where each UE 100 performs D2D communication in a connectedstate will be mainly described.

As illustrated in FIG. 11, in step S121, a UE 100-1 to a UE 100-3, whichare in a connected state to a cell of an eNB 200, perform D2Dcommunication.

In step S122, the UE 100-1 transmits a D2D termination preliminarynotification indicating that termination of D2D communication is wishedto the UE 100-2 and the UE 100-3 during the D2D communication.

The UE 100-2 and the UE 100-3 which have been received the D2Dtermination preliminary notification determine whether D2D communicationwith the UE 100-1 is wished to be continued. In this case, a descriptionwill be given under the assumption that the UE 100-2 and the UE 100-3 donot wish continuity of D2D communication with the UE 100-1.

In step S123, the UE 100-2 and the UE 100-3 transmit a D2D terminationpermission notification permitting termination of the D2D communicationto the UE 100-1.

In step S124-1, the UE 100-1, which has received the D2D terminationpermission notification from the UE 100-2 and the UE 100-3 transmits aD2D termination completion notification indicating completion ofprocessing to terminate the D2D communication to the eNB 200. Also, instep S124-2, the UE 100-1 terminates the D2D communication. The eNB 200,which has received the D2D termination completion notification from theUE 100-1, can terminate control of the D2D communication (resourceallocation or the like) for the UE 100-1.

On the other hand, in step S125, the UE 100-2 and the UE 100-3 continuethe D2D communication.

Second Embodiment

Next, the second embodiment will be described while focusing ondifferences from the first embodiment. A system configuration accordingto a second embodiment is identical to that of the first embodiment.

(1) Operation Overview

In the second embodiment, the UE 100-1 measures a D2D communication timeindicating a time during which D2D communication is continued, or a D2Ddata amount indicating an amount of data transmitted and/or received inD2D communication. When the UE 100-1 terminates the D2D communication,the UE 100-1 transmits D2D measurement information indicating at leastone of the D2D communication time and the D2D data amount to a network.Therefore, the network can grasp at least one of the D2D communicationtime and the D2D data amount in the D2D communication in which a datapath does not pass through the network, and therefore, can appropriatelyperform charging for the

D2D communication, or the like.

(2) Operation Sequence

FIG. 12 is a sequence diagram illustrating an operation according to asecond embodiment.

As illustrated in FIG. 12, in step S201, a UE 100-1 starts D2Dcommunication. Also, the UE 100-1 starts measurement of a D2Dcommunication time or a D2D data amount.

In step S202, the UE 100-1 terminates the D2D communication. Also, theUE 100-1 terminates the measurement of the D2D communication time or theD2D data amount.

In step S203, the UE 100-1 transmits the D2D measurement informationindicating at least one of the D2D communication time and the D2D dataamount which are measured to the network (eNB 200).

In the case of performing the D2D communication in a connected state,the UE 100-1 may transmit the D2D measurement information to thenetwork, in response to reception of a transmission request of the D2Dmeasurement information from the network.

In the case of performing the D2D communication in an idle state, it ispossible to apply change the sequence of FIG. 12 as described below.

The UE 100-1 transmits the D2D measurement information to the networkonly when performing the D2D communication by using a frequency bandwhich is managed by an operator. Therefore, the network can performcharging control in which charging is not made with respect to afrequency band which is not managed.

When transited to a connected state so as to perform cellularcommunication after termination of the D2D communication, the UE 100-1may transmit the D2D measurement information to the network. Therefore,it is possible to prevent transition to the connected state only inorder to transmit the D2D measurement information.

The UE 100-1 holds the D2D measurement information until the D2Dmeasurement information can be transmitted to a network. In this case,the UE 100-1 may include a time stamp related to a measurement timepoint of the D2D measurement information in the D2D measurementinformation. Therefore, it is possible to perform charging control, suchas performing charging differently dependent on time zones in which theD2D communication is performed. The time stamp may be a start time pointof the D2D communication and/or an elapsed time from a termination timepoint.

The UE 100-1, which holds the D2D measurement information, storesinformation on an operator that manages frequency bands used for the D2Dcommunication. When connected to a network (eNB 200) of the operator,the UE 100-1 may transmit the D2D measurement information to thenetwork. Therefore, it is possible to limit a transmission destinationof the D2D measurement information to an appropriate operator network.

It should be noted that the UE 100-1 may transit to the connected stateimmediately after termination of the D2D communication and transmit theD2D measurement information to the network, without holding the D2Dmeasurement information.

Third Embodiment

Next, the third embodiment will be described while focusing on thedifferences from the first embodiment and the second embodiment. Asystem configuration according to a third embodiment is identical tothat of the first embodiment.

(1) Operation Overview

In the third embodiment, there is an anchor UE which representativelyperforms communication with a network for D2D communication. The anchorUE is a UE 100-2 or another user terminal which performs D2Dcommunication.

The anchor UE may be a UE 100 designated by a network from among aplurality of UEs 100 (hereinafter, referred to as a “D2D UE group”)which performs D2D communication, or a UE 100 autonomously selected fromthe D2D UE group according to a certain selection criterion. In thiscase, the selection criterion is, for example, a criterion of selectinga UE 100 having the smallest or largest UE identifier. Alternatively, inthe case of performing the D2D communication in a connected state, theselection criterion may be a criterion of selecting a UE 100 having thesmallest or largest C-RNTI. In a case in which the anchor UE isautonomously selected based on the selection criterion, when a UE 100which is suitable for the anchor UE is included in the D2D UE group, theanchor UE may be changed or may not be changed.

In the third embodiment, the UE 100-1 transmits a D2D terminationpreliminary notification to a UE 100-2 through the anchor UE. The UE100-2 transmits a D2D continuity request to a UE 100-1 through theanchor UE.

In the third embodiment, the UE 100-1 transmits a D2D terminationpreliminary notification to a UE 100-2 through the anchor UE. The UE100-2 transmits a D2D termination permission notification to a UE 100-1through the anchor UE.

In the third embodiment, the UE 100-1 may measure a D2D communicationtime indicating a time during which D2D communication is continued, or aD2D data amount indicating an amount of data transmitted and/or receivedin D2D communication, like the second embodiment. When the UE 100-1terminates the D2D communication, the UE 100-1 transmits D2D measurementinformation indicating at least one of the D2D communication time andthe D2D data amount to the anchor UE. The anchor UE transmits the D2Dmeasurement information to the network in response to reception of theD2D measurement information. Also, when the anchor UE is changed, anoriginal anchor UE may transmit the D2D measurement information to a newanchor UE. In this way, the new anchor UE can transmit the D2Dmeasurement information, to which D2D communication situations so far isreflected, to the network.

(2) Operation Pattern 1

FIG. 13 is a sequence diagram illustrating an operation pattern 1according to a third embodiment. In this case, it is assumed that eachUE 100 performs D2D communication in an idle state. Also, a UE 100-3 isan anchor UE in a D2D UE group including a UE 100-1 to UE 100-3.

As illustrated in FIG. 13, in step S301, the UE 100-1 to the UE 100-3which are in an idle state perform D2D communication.

In step S302, the UE 100-1 transmits a D2D termination preliminarynotification representing that termination of D2D communication iswished to the UE 100-3 during the D2D communication. Also, when the UE100-1 transmits a D2D termination preliminary notification, the UE 100-1starts a timer corresponding to a second predetermined period. The UE100-3 transmits the D2D termination preliminary notification receivedfrom the UE 100-1 to the UE 100-2.

The UE 100-2 and the UE 100-3 which have been received the D2Dtermination preliminary notification determine whether D2D communicationwith the UE 100-1 is wished to be continued. In this case, a descriptionwill be given under the assumption that the UE 100-2 and the UE 100-3 donot wish D2D communication with the UE 100-1 to be continued.

In step S303, when confirming that the timer corresponding to the secondpredetermined period is expired, the UE 100-1 terminates the D2Dcommunication.

On the other hand, in step S304, the UE 100-2 and the UE 100-3 continuethe D2D communication.

Although it is assumed in FIG. 13 that the UE 100 performs the D2Dcommunication in an idle state, the sequence of FIG. 13 may be changedin a case where the UE 100 performs the D2D communication in aconnection state. Specifically, when confirming that a timercorresponding to a second predetermined period is expired, the UE 100-1transmits a D2D termination completion notification indicatingcompletion of processing to terminate the D2D communication to thenetwork (eNB 200). Alternatively, the UE 100-1 may transmit the D2Dtermination preliminary notification to the network through the anchorUE (UE 100-3). Then, the UE 100-1 terminates the D2D communication.

(3) Operation Pattern 2

FIG. 14 is a sequence diagram illustrating an operation pattern 2according to a third embodiment. In this case, it is assumed that eachUE 100 performs D2D communication in an idle state or a connected state.A UE 100-3 is an anchor UE in a D2D UE group including a UE 100-1 to UE100-3. Also, a description for the same operation as FIG. 13 will beappropriately omitted.

As illustrated in FIG. 14, in step S311, a UE 100-1 to a UE 100-3perform D2D communication.

In step S312, the UE 100-1 transmits a D2D termination preliminarynotification indicating that termination of D2D communication is wishedto the UE 100-3 during the D2D communication. The UE 100-3 transmits theD2D termination preliminary notification received from the UE 100-1 tothe UE 100-2.

The UE 100-2 and the UE 100-3 which have been received the D2Dtermination preliminary notification determine whether D2D communicationwith the UE 100-1 is wished to be continued. In this case, a descriptionwill be given under the assumption that the UE 100-2 wishes continuityof D2D communication with the UE 100-1.

In step S313, the UE 100-2 transmits a D2D continuity request requestingcontinuity of the D2D communication to the UE 100-3. The UE 100-3transmits a D2D continuity request received from the UE 100-2 to the UE100-1. The UE 100-1, which has received the D2D continuity request,determines to continue the D2D communication without termination of theD2D communication according to a wish from the UE 100-2. Also, when theUE 100-1 receives the D2D continuity request, the UE 100-1 starts atimer corresponding to a first predetermined period. The UE 100-1, whichhas received the D2D continuity request, is prohibited from transmittinga D2D termination preliminary notification until the first predeterminedperiod has elapsed after reception of the D2D continuity request.

In step S314, the UE 100-1 to the UE 100-3 continue the D2Dcommunication.

(4) Operation Pattern 3

FIG. 15 is a sequence diagram illustrating an operation pattern 3according to a third embodiment. In this case, it is assumed that eachUE 100 performs D2D communication in an idle state. A UE 100-3 is ananchor UE in a D2D UE group including a UE 100-1 to UE 100-3. Also, adescription for the same operation as FIG. 13 will be appropriatelyomitted.

As illustrated in FIG. 15, in step S321, the UE 100-1 to the UE 100-3which are in an idle state perform D2D communication.

In step S322, the UE 100-1 transmits a D2D termination preliminarynotification indicating that termination of D2D communication is wishedto the UE 100-3 during the D2D communication. The UE 100-3 transmits theD2D termination preliminary notification received from the UE 100-1 tothe UE 100-2. Also, in the operation pattern 3, when the UE 100-1transmits the D2D termination preliminary notification, the UE 100-1 maynot start a timer corresponding to a second predetermined period.

The UE 100-2 and the UE 100-3 which have been received the D2Dtermination preliminary notification determine whether D2D communicationwith the UE 100-1 is wished to be continued. In this case, a descriptionwill be given under the assumption that the UE 100-2 and the UE 100-3 donot wish continuity of D2D communication with the UE 100-1.

In step S323, the UE 100-2 transmits a D2D termination permissionnotification permitting termination of the D2D communication to the UE100-3. The UE 100-3 transmits the D2D termination permissionnotification received from the UE 100-2 to the UE 100-1.

In step S324, the UE 100-1, which has received the D2D terminationpermission notification terminates the D2D communication.

On the other hand, in step S325, the UE 100-2 and the UE 100-3 continuethe D2D communication.

Although it is assumed in FIG. 15 that the UE 100 performs the D2Dcommunication in an idle state, the sequence of FIG. 15 may be changedin a case where the UE 100 performs the D2D communication in aconnection state. Specifically, the UE 100-1, which has received the D2Dtermination permission notification, transmits the D2D terminationcompletion notification indicating completion of processing to terminatethe D2D communication to the network (eNB 200). Alternatively, the UE100-1 may transmit the D2D termination preliminary notification to thenetwork through the anchor UE (UE 100-3). Then, the UE 100-1 terminatesthe D2D communication.

OTHER EMBODIMENTS

The above-described embodiments are not limited to be performedindividually and independently. They may be performed in a combinationthereof.

In addition, in the above-described embodiments, the LTE system as oneexample of a cellular system is described; however, the presentinvention is not limited to the LTE system, and the present inventionmay be applied to a communication system other than the LTE system.

In addition, the entire content of Japanese Patent Application No.2013-134377 (filed on Jun. 26, 2013) is incorporated in the presentspecification by reference.

INDUSTRIAL APPLICABILITY

According to the present invention, it provides the base station, theuser terminal, and the processor which can prevent the user terminalfrom performing useless processing by termination of D2D communicationof a counterpart terminal in D2D communication.

1. A mobile communication system comprising: a first user terminal and asecond user terminal configured to perform D2D (Device to Device)communication that is direct device to device communication, wherein thefirst user terminal transmits a D2D termination preliminary notificationindicating that the first user terminal wishes termination of the D2Dcommunication to the second user terminal during the D2D communication,and the first user terminal terminates the D2D communication aftertransmitting the D2D termination preliminary notification.
 2. The mobilecommunication system according to claim 1, wherein the first userterminal transmits the D2D termination preliminary notification whendata to be transmitted to the second user does not exist in the D2Dcommunication.
 3. The mobile communication system according to claim 2,wherein a case where data to be transmitted does not exist is a casewhere the first user terminal terminates an application used in the D2Dcommunication.
 4. The mobile communication system according to claim 1,wherein the second user terminal, which has received the D2D terminationpreliminary notification, transmits a D2D continuity request requestingcontinuity of the D2D communication to the first user terminal when itis determined that continuity of the D2D communication is wished.
 5. Themobile communication system according to claim 4, wherein the seconduser terminal, which has received the D2D termination preliminarynotification, determines that continuity of the D2D communication iswished, when data to be transmitted to the first user terminal exists orwhen the second user terminal is waiting for reception of a specificsignal associated with the first user terminal.
 6. The mobilecommunication system according to claim 4, wherein the first userterminal, which has received the D2D continuity request, is prohibitedfrom transmitting the D2D termination preliminary notification until afirst predetermined period has elapsed after reception of the D2Dcontinuity request.
 7. The mobile communication system according toclaim 4, wherein the first user terminal terminates the D2Dcommunication when the first user terminal does not receive the D2Dcontinuity request until the second predetermined period has elapsedafter transmission of the D2D termination preliminary notification. 8.The mobile communication system according to claim 1, wherein the seconduser terminal, which has received the D2D termination preliminarynotification, transmits a D2D termination permission notificationpermitting termination of the D2D communication to the first userterminal when the second user terminal permits the first user terminalto terminate the D2D communication.
 9. The mobile communication systemaccording to claim 1, wherein the first user terminal measures a D2Dcommunication time indicating a time during which the D2D communicationis continued, or a D2D data amount indicating an amount of datatransmitted and/or received in the D2D communication, and the first userterminal transmits D2D measurement information indicating at least oneof the D2D communication time and the D2D data amount to a network, whenthe first user terminal terminates the D2D communication.
 10. The mobilecommunication system according to claim 9, wherein the first userterminal measures the D2D communication time or the D2D data amount whenperforming the D2D communication by using a frequency band managed by anoperator.
 11. The mobile communication system according to claim 1,comprising an anchor terminal configured to representatively performcommunication with a network for the D2D communication, wherein theanchor terminal is the second user terminal or another user terminalwhich performs the D2D communication, the first user terminal measures aD2D communication time indicating a time during which the D2Dcommunication is continued, or a D2D data amount indicating an amount ofdata transmitted and/or received in the D2D communication, and the firstuser terminal transmits D2D measurement information indicating at leastone of the D2D communication time and the D2D data amount to the anchorterminal, when the first user terminal terminates the D2D communication.12. The mobile communication system according to claim 4, comprising ananchor terminal configured to representatively perform communicationwith a network for the D2D communication, wherein the anchor terminal isanother user terminal which performs the D2D communication, the firstuser terminal transmits the D2D termination preliminary notification tothe second user terminal through the anchor terminal, and the seconduser terminal transmits the D2D continuity request to the first userterminal through the anchor terminal.
 13. The mobile communicationsystem according to claim 8, comprising an anchor terminal configured torepresentatively perform communication with a network for the D2Dcommunication, wherein the anchor terminal is another user terminalwhich performs the D2D communication, the first user terminal transmitsthe D2D termination preliminary notification to the second user terminalthrough the anchor terminal, and the second user terminal transmits theD2D termination permission notification to the first user terminalthrough the anchor terminal.
 14. A user terminal which performs D2D(Device to Device) communication that is direct device to devicecommunication with another user terminal, comprising: a controllerconfigured to transmit a D2D termination preliminary notificationindicating that the user terminal wishes termination of the D2Dcommunication to the another user terminal during the D2D communication,wherein the controller terminates the D2D communication aftertransmitting the D2D termination preliminary notification.
 15. Aprocessor, which is provided in a user terminal configured to performD2D (Device to Device) communication that is direct device to devicecommunication with another user terminal, wherein the processorperforms: a process of transmitting a D2D termination preliminarynotification indicating that the user terminal wishes termination of theD2D communication to the another user terminal during the D2Dcommunication; and a process of terminating the D2D communication aftertransmission of the D2D termination preliminary notification.